1. Field of the Invention
The invention relates to a backlight unit, and more particularly to a backlight unit for improving assembly efficiency and reducing light guide plate damage.
2. Description of the Related Art
FIG. 1A is a three dimensional diagram schematically showing a conventional backlight unit of liquid crystal display. As shown in FIG. 1A, the conventional backlight unit has a frame 10, a light guide plate 40 and a reflector 30. The reflector 30 is connected to the frame 10 by fixing the screws 35 in the screw holes (not shown in the drawing) positioned on the frame 10.
FIG. 1B is an exploded diagram of FIG. 1A showing the structure of the conventional backlight unit. As shown in FIG. 1B, a reflecting sheet 20 is positioned above the frame 10. The light guide plate 40 is positioned on the reflecting sheet 20, The light guide plate 40 has a pair of protrusions 42 of the light guide plate 40 inserted in the grooves 12 of the frame 10. A lamp 34 is installed inside the reflector 30, and then the screws 35 are positioned into the screw holes 15 of the frame 10 so as to combine the two sides 32 of the reflector 30 with the frame 10. Finally, the backlight unit is accomplished after installing a diffusing device 50 on the light guide plate 40. The diffusing device 50 includes a diffusing sheet 52, a prism sheet 54 and a protecting film 56. A display panel, such as a liquid crystal panel 60, is combined with the backlight unit to form a display deice, such as a liquid crystal display.
Referring to FIG. 1B, the frame 10 has three arms, and the openings of the grooves 12 face upward. The light guide plate is fixed with three sides of the frame 10, so the supporting force of the frame is insufficient. Thus, this design is insufficient to protect the light guide plate.
FIG. 1C shows another frame 11. The frame 11 has four arms to prevent it from distortion and to increase the force for fixing the light guide plate. One arm 111 of the frame 11 has a groove 13, and the opening of the groove 13 faces toward the light guide plate 40. When the light guide plate is combined with the frame 11, the frame 11 is distorted in order to install the protrusion 42 of the light guide plate 40 into the groove 13 of the frame 11. However, as the force goes beyond the limit, the frame 11 is deformed and damages the light guide plate 40 and the diffusing device 50.
The light guide plate easily departs from the frame when the conventional backlight unit is jarred or positioned upside down. In the same time, the surface of the light guide plate is scraped easily, and the distance between the lamp and the light guide plate is changed easily to influence optical properties.
To solve the above problems, it is an object of the present invention to provide a frame of a backlight unit in a liquid crystal display. The frame includes a fixing arm. The fixing arm comprises a fixing portion, a first groove, and a second groove. The fixing portion has a first fixing side and a fixing second side, the first groove has a first end, and the second groove has a second end. The first groove is connected with the fixing portion, and the first fixing side of the fixing portion is aligned to the first end of the first groove. The second groove is connected with the fixing portion, and the second fixing side of the fixing portion is aligned to the second end of the second groove.
In addition, the first groove has a third end, the second groove has a fourth end. The first groove has a first distance between the first end and the third end, the second groove has a second distance between the second end and fourth end, and the fixing portion has a third distance between the first and the second fixing sides. The sum of the first and second distances is not less than the third distance. The first distance is smaller than the third distance, and the second distance is smaller than the third distance.
Further, the frame for fixing a light guide plate includes two opposite fixing arms. Each fixing arm has a first groove, a first fixing pin, a second groove, and a second fixing pin. The first groove has a first opening, and the second groove has a second opening. The first fixing pin has a fourth distance to the first opening, the second fixing pin has a fifth distance to the second opening, and a sum of the fourth and fifth distances is larger than a thickness of the frame.
The fixing portion is formed between the first groove and the second groove. The fixing portion has a fixing portion length, the first fixing pin has a first pin length, the second fixing length has a second pin length, and a sum of the first pin length and the second pin length is not greater than the fixing portion length.
The invention also includes a backlight unit for a liquid crystal display. The backlight unit includes at least a light guide plate and a frame. The light guide plate has a light-incident surface, a light-reflecting surface, and two side surfaces formed at both sides of the light-incident surface. Each side surface has a protrusion. The frame comprises two opposite fixing arms, and each fixing arm has a first groove, a second groove and a fixing portion. The first groove has a first end, the second groove has a second end, and the fixed portion has a first fixing side and a second fixing side. The first fixing side of the fixing portion is aligned to the first end of the first groove, and the second fixing side of the fixing portion is aligned to the second end of the second groove. The light guide plate is combined with the frame by gliding and inserting the protrusion into the fixing portion through the first and second grooves. The first groove has a third end, the second groove has a fourth end, the first groove has a first distance between the first end and the third end, the second groove has a second distance between the second end and fourth end, the fixing portion has a third distance between the first and second fixing sides, and a sum of the first and second distances is not less than the third distance. The first distance is smaller than the third distance, and the second distance is smaller than the third distance. Each fixing arm comprises a first fixing pin and a second fixing pin, the first groove has a first opening, the second groove has a second opening, the frame has a thickness, the first fixing pin has a sixth distance to the first opening, the second fixing pin has a seventh distance to the second opening, and a sum of the sixth and seventh distances is larger than the thickness of the frame. A first pin length of the first fixing pin plus a second pin length of the second fixing pin is not greater than the third distance of the fixing portion. A height of each protrusion is not greater than a thickness of the light guide plate. The backlight unit for a liquid crystal display further includes a reflector having a reflecting surface toward the light-incident surface of the light guide plate, and a light source installed within the reflector. The reflector reflects lights of the light source. The backlight unit also includes a reflecting sheet positioned under the light guide plate and a diffusing device located above the light guide plate. The diffusing device has a diffusing sheet, a prism sheet and a protecting film, and the protecting film is adjacent to the light guide plate.
The invention also includes another backlight unit for a liquid crystal display. The backlight unit has a light guide plate having a side surface, a protrusion formed on the side surface, and a frame having a height H. The frame has a first groove with a first height h1 and a first width d1, and a second groove with a second height h2 and a second width d2. The frame also has a fixing portion with a third height h3 and a third width D. The third width D of the fixing portion is not greater than a sum of the first width d1 and the second width d2. The height H of the frame is not greater than a sum of the first is height h1, the second height h2, and the third height h3. The light guide plate is combined with the frame by gliding and inserting the protrusion into the fixing portion through the first and second grooves.
In addition, the protrusion has a fourth height h4 and a fourth width d4, the fourth width d4 is not greater than the third width D, and the fourth height h4 is not greater than the third height h3. The fourth height h4 is not greater than a thickness of the light guide plate.